Self-assembly of carbon-nanotube-based single electron memories

TL;DR

This paper presents a scalable method for integrating carbon nanotube-based single electron memories, demonstrating reproducible single-electron transfer behavior with long retention times at cryogenic temperatures.

Contribution

It introduces a complete self-assembly process for wafer-scale integration of carbon nanotube memories with high yield and functionalized gold beads acting as storage nodes.

Findings

Reproducible hysteresis steps in transfer characteristics at low temperatures.

Capacitance measurements confirm single-electron transfer mechanism.

Memory retention exceeds 550 seconds at 1.5K.

Abstract

We demonstrate wafer-scale integration of single electron memories based on carbon nanotube field effect transistors (cnfets) by a complete self assembly process. First, a dry self assembly based on a Hot Filament assisted Chemical Vapor Deposition technique allows both localized growth and in situ electrical connection of carbon nanotubes on predefined catalytic electrodes. The semiconducting carbon nanotubes integration yield can exceed 50% for a batch. Secondly, a wet self-assembly attaches single 30 nm-diameter gold bead in the nanotube vicinity via chemical functionalization. The bead acts as the memory storage node while the cnfet operated in the subthreshold regime is an electrometer having exponential gain. Below 50 K, the transfer characteristics of some functionalized cnfets show highly reproducible hysteretical steps whose height can reach one decade of current. Evaluation of the capacitance confirms these current steps originate from single electron transfers between the bead and the nanotubes with a time retention exceeding 550s at 1.5K.